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Public Health Official: A ten-year study found that adults consuming over 400 milligrams daily of compound Q—a synthetic preservative in processed foods—had a 40 percent higher incidence of chronic kidney disease (CKD) than those consuming under 50 milligrams daily. The authors concluded that compound Q directly causes CKD. This is highly suspect. Compound Q is prevalent in convenience foods heavily relied upon by people in "food deserts" lacking fresh produce. Residing in a food desert correlates strongly with lower socioeconomic status (SES), which is a major independent risk factor for CKD. Therefore, the higher CKD incidence among heavy compound Q consumers is almost certainly a byproduct of SES disparities rather than the chemical itself.

Which of the following, if true, most strongly supports the public health official's conclusion?

  1. A
    The longitudinal study failed to adequately control for the participants' baseline kidney function at the start of the ten-year observation period.
  2. B
    Regular consumption of ultra-processed convenience foods that lack compound Q is not associated with an increased incidence of chronic kidney disease among individuals in lower socioeconomic brackets.
  3. Among study participants belonging to the same socioeconomic bracket, those who consumed more than 400 milligrams of compound Q daily did not exhibit a higher incidence of CKD than those who consumed less than 50 milligrams daily.Answer
  4. D
    Only individuals who have a lower socioeconomic status will ever suffer from the chronic stress that leads to delayed medical care.
  5. E
    Most synthetic preservatives found in ultra-processed convenience foods are significantly less expensive for manufacturers to produce than compound Q.

Answer

The statement showing that within the same socioeconomic bracket, varying levels of compound Q consumption do not change the incidence of CKD.
The public health official argues that a correlation between compound Q and CKD is actually driven by a third confounding variable: socioeconomic status (SES). To strengthen this claim, one must demonstrate that compound Q has no causal power independent of SES. The correct answer achieves this by holding SES constant; it shows that among people with the same SES, consuming large amounts of compound Q does not lead to higher rates of CKD. This isolates the variables and proves that the original correlation was indeed merely a byproduct of SES disparities.

Step-by-Step Solution

1
Analyze the logical structure of the stimulus.
Identify the conclusion: The higher CKD incidence is caused by SES disparities, not compound Q. Identify the premises: The study shows a correlation between compound Q and CKD. However, heavy compound Q consumers live in food deserts, which correlates with low SES, a known independent risk factor for CKD.
Understanding the exact causal claim being made is necessary before attempting to strengthen it.
2
Identify the reasoning gap or causal vulnerability.
The official assumes that just because a plausible alternative cause (SES) exists, the original proposed cause (compound Q) must be blameless. To strengthen this, evidence must be found that isolates the variables and proves compound Q is indeed harmless.
Strengthening a claim of an alternative cause often requires demonstrating that when the alternative cause is controlled for, the original correlation disappears.
3
Evaluate the options against the identified logical gap.
The correct option must hold the confounding variable (SES) constant. The option stating that participants in the same SES bracket showed no difference in CKD rates regardless of compound Q consumption achieves exactly this.
This rules out compound Q as the active causal agent, completely validating the official's alternative causal hypothesis.

Key Concept

Causal Reasoning: Alternative Causes and Controlling Variables
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